The compression of gaseous oxygen to produce pressurized oxygen gas is very expensive when compared to the cost of compression of other atmospheric gases. The cost is higher in both power consumed and in initial capital cost of the compression equipment. This high cost is due to the reactive nature of gaseous oxygen. Mechanical tolerances are set much looser for an oxygen compressor than for a nitrogen or air compressor so as to reduce the risk of a rub within the machine that could cause a fire. These looser tolerances or high clearances result in significantly reduced compressor efficiencies, on the order of six to ten percent. This lower efficiency corresponds to a higher compressor power.
The problem of high cost in the production of pressurized oxygen gas is not acute when the oxygen is produced by the cryogenic separation of air because the oxygen can be recovered as high pressure gas directly from a column, or can be taken from a column as liquid, pressurized and then vaporized. However these expediencies are not available when the oxygen is produced by a non-cryogenic air separation method such as by vacuum pressure swing adsorption.
Those skilled in the art have addressed this problem by making small, incremental improvements in oxygen compressors. Incremental improvements in centrifugal compressors have been achieved, but the gains have been modest. Positive displacement machines have been used in place of centrifugal compressors, and while they have a lower initial capital cost, the life cycle cost of such machines is higher due to increased power consumption and higher maintenance cost. In summary, improvements in such machines over the years has been only incremental, not a step change.
In the operation of a non-cryogenic oxygen plant, such as a vacuum pressure swing adsorption plant, the cost of the oxygen compressor is a significant portion of both the total capital cost and the power usage of the plant. If a significant reduction in the cost of oxygen compression can be achieved, a substantial decrease in the total cost of a non-cryogenic oxygen production plant can be attained.
Accordingly it is an object of this invention to provide an improved system for the production of pressurized oxygen gas.
It is another object of this invention to provide a system for the production of pressurized oxygen gas from low pressure oxygen gas without the need for employing an oxygen compressor.